How to Detect Duplicate Elements in a PHP Array in O(n) Time

Detecting duplicate elements in an array requires scanning each element and checking if it appears more than once. The problem is defined as: given an integer array nums, return true if any value occurs at least twice, otherwise return false.

Example

Input: nums = [1,2,3,1]
Output: true

Input: nums = [1,2,3,4]
Output: false

PHP Solution

The following PHP class implements the required functionality:

class Solution {
    /**
     * @param Integer[] $nums
     * @return Boolean
     */
    function containsDuplicate($nums) {
        $map = array();
        foreach ($nums as $n => $i) {
            if (array_key_exists($i, $map)) {
                return true;
            }
            $map[$i] = $n;
        }
        return false;
    }
}

Function Execution Flow

Initialize an empty associative array $map to store elements that have been seen.

Iterate over each element $i in $nums.

Check if $i already exists as a key in $map.

If it does, a duplicate is found and the function returns true immediately.

If not, store the element in $map with its index for future checks.

If the loop finishes without finding a duplicate, return false.

Time and Space Complexity

Time complexity: O(n), where n is the number of elements in the input array. Each element is examined once.

Space complexity: O(n) in the worst case, because the associative array may store all unique elements.

Conclusion

The optimized PHP solution leverages an associative array for constant‑time lookups, enabling fast and reliable detection of duplicate values in an array while maintaining linear time and space performance.